This sounds great!
Regarding Admob, it would be great to see Admob used as the Ad network aggregator.
A single Admob C++ .h interface created that has separate .cpp implementation files for iOS, Android and WP8.1.
Each implementation would then tie into the ObjC, Java and C# of the platform as needed.
The Objc, Java and c# could handle the callbacks for ad network prioritization on each platform.
The Admob web app could be used to manage ad network prioritization.
The c++ file could then present the showAd, hideAd, loadAd, and callbacks for interstitial lifecycle and add loading/failing through a simple interface.
For iOS and Android, it could then be configured to call Chartboost, Vungle, AdColony, Applovin, or others as primary and use Admob to backfill. This would provide a maximum fill rate and enable tweaking network prioritization in the Admob web app.
By the way, while Vungle and AdColony do have great payout on their video ads, but they do gouge the revenue share if you don't serve a critical mass of ads for them. I forget exactly what that critical mass is, but it was something like less than 5,000,000 ads a month and you get 20% less revenue share. I just looked at Vungle and Adcolony's sites and I cannot find the legal document that I read that in. But my point is that having Admob as a mediator enables some control over which ads are served and can be changed at any time.
A setup like this could do a great job of maximizing ad revenue in ones game.